Various technologies are known for monitoring the position or relative position of an object or group of objects. One technology equips an implement with a tuned circuit and places the implement in proximity to a tablet having coils extending in two coordinate directions. The tablet coils are sequentially excited with AC energy having approximately the same frequency as the resonant frequency of the tuned circuit. The excitation causes the tuned circuit to interact with and change the AC current flowing in the coils of the tablet. The AC current flowing in the coils of the tablet changes as a function of the position of the tuned circuit and therefore, with the position of the implement, with the current experiencing the greatest changes in those coils closest to the implement. The changes in the current are measured and interpolated to determine the position of the implement. One version of this technology tracks at least two implements at the same time.
In some circumstances, the absolute location of an object is less important than its relationship to other objects. For example, various technologies are suited to counting the number of objects in a set of objects. For example, one approach equips each object with an easily-recognizable marker such as a bar code, a reflective tag, or a colored dot. Then, an automated vision system receives an image of the set and counts the number of markers in the image to determine the number of objects in the set. This system has its failings. For example, a marker on one object may be obscured by dirt or by another object. Changing the orientation of the object, e.g., such that the marker faces away from the camera, may render this system inaccurate or may otherwise hinder the operation of the system. Another approach utilizes scales calibrated to the weight of a single object, providing a count of the number of objects on the scale and their spatial location, but this approach may provide poor spatial resolution relative to the size of the object.
A need therefore exists for improved apparatus and methods capable of counting the number of objects in a set or determining the position or relative position of the objects in the set. In light of general public concern over privacy issues regarding electromagnetic tagging, it would be desirable to have a technology that provides automated counting and tracking functions without using electronic chips and individual ID numbers.